import math
x1,y1,x2,y2 = map(float,raw_input().split())
r = math.sqrt(abs((x1-x2)**2+(y1-y2)**2))
print r import math math x1,y1,x2,y2 = map(float,raw_input().split()) x1 map(float,raw_input().split()) map float raw_input().split() ().split () raw_input split y1 x2 y2 r = math.sqrt(abs((x1-x2)**2+(y1-y2)**2)) r math.sqrt(abs((x1-x2)**2+(y1-y2)**2)) math.sqrt math sqrt abs((x1-x2)**2+(y1-y2)**2) abs (x1-x2)**2+(y1-y2)**2 (x1-x2)**2 x1-x2 x1 x2 2 (y1-y2)**2 y1-y2 y1 y2 2 print x1,y1,x2,y2 = map(float,raw_input().split()) map(float,raw_input().split()) x1 r = math.sqrt(abs((x1-x2)**2+(y1-y2)**2)) math.sqrt(abs((x1-x2)**2+(y1-y2)**2)) r y2 = map(float,raw_input().split()) map(float,raw_input().split()) y2 y1,x2,y2 = map(float,raw_input().split()) map(float,raw_input().split()) y1 x2,y2 = map(float,raw_input().split()) map(float,raw_input().split()) x2
import math
x1,y1,x2,y2 = map(float,raw_input().split())
r = math.sqrt(abs((x1-x2)**2+(y1-y2)**2))
print r